Systematic Evolution of Resonant Coupling Behavior Between Surface Plasmon Polaritons and Multi-waveguide Modes in Metal-Dielectric Multi-layers

A multi-layer structure consisting of metal and dielectric layers which allows coupling between surface plasmon polaritons and waveguide modes is studied by calculating reflectivity curves of incident light. A wide waveguide structure is employed to ensure SPP resonance with different order waveguide modes when varying coupling layer thicknesses. Multi-hybrid plasmonic waveguide modes (HPWG) are formed in the coupled system. The weight fractions of metal SPP deduced from losses of HPWG modes are calculated for each hybridized mode, which can be considered as a parameter of evaluating coupling strength. Three different evolution stages for hybrid modes are clearly distinguished based on the variation of loss with spacer layer thickness. The interaction between SPP and waveguide experiences a series of change from weak Fano resonance, via strong coupling, finally to weak coupling process. In case of strong coupling regime, the contribution of metal SPP for low order hybrid modes starts to increase and then decreases with decreasing spacer layer thicknesses. Furthermore, difference of resonant behavior for hybrid modes in both weak coupling stages is analyzed in detail.